yeah Long, the trick is to bring the leg over the arm like an omoplata but not scooting your hips out. by keeping the arm trapped, they can't pass your guard, then stick yer fott/shin under their chin and hey presto. works for me anyway

I only know it as a good escape from north/south position otherwise I always prefer position over submission. Kind of boring but my instructor is a traditional BJJ guy, we believe gaining the mount is the best/worst thing that can happen and never give away position.

This is why we don't go for many leg/ankle submissions because you drop back giving your opponent to many options for escape or their own subs. If you got the position to go for a leg sub then normally you can get a better position as an alternative.

Back on the subject, it fucking hurts if your foot gets stuck and all your toes get bent up!